JPH06305837A - Sintered silicon nitride - Google Patents

Abstract

(57) [Abstract] [Purpose] The product has sufficient strength as a structural material for machine parts, has high reliability with little variation in strength, and has excellent cutting performance as a cutting tool, thus improving productivity and cost. Also in terms of the above, a silicon nitride-based sintered body that is excellent is provided. [Structure] Columnar and equiaxed crystal grains of Si ₃ N ₄ and / or sialon, a grain boundary phase existing between these crystal grains, and dispersed particles dispersed in the grain boundary phase. ,
The average minor axis diameter of the columnar crystal grains is 0.3 μm or less and the average major axis diameter is 5 μm or less, and the average grain diameter of the equiaxed crystal grains is 0.1 μm or less.
5 μm or less, the average particle diameter of dispersed particles is 0.1 μm or less, and the volume of dispersed particles is 0.05 vol% or more when the total volume of other sintered body structures is 1. Sintered body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body which has excellent mechanical strength at room temperature, has a small variation, and is excellent in productivity and cost.

[0002]

2. Description of the Related Art Since silicon nitride is a material having a well-balanced strength, fracture toughness value, corrosion resistance, wear resistance, thermal shock resistance, oxidation resistance, etc., it is used for cutting tools, sliding parts and other mechanical structures. Although it is used in a wide range of materials, it has a problem that it is inferior to metal materials in terms of strength and reliability.

One of the causes of the strength deterioration in such a silicon nitride sintered body is the problem of the grain boundary phase existing inside the sintered body structure. This grain boundary phase is made of a glassy material derived from a sintering aid indispensable for the sintering of silicon nitride, and is generally more brittle than the matrix of silicon nitride, so it is easy to break when stress is applied to the grain boundary phase, It is a major cause of strength deterioration of silicon nitride-based sintered bodies.

Therefore, various methods have been attempted for improving the strength by reducing the grain boundary phase of the silicon nitride sintered body. For example, in Japanese Patent Laid-Open No. 3-117315, a fine structure including columnar crystal grains of α-Si ₃ N ₄ and equiaxed crystal grains of β-Si ₃ N ₄ is used to reduce the thickness of grain boundary phase. A method of causing is disclosed. However, in order to make α crystal grains finer, it is necessary to add fine Si ₃
Since it is necessary to use N ₄ powder, there is a drawback that the cost becomes high. In addition, since excellent strength characteristics cannot be obtained unless the β ratio is increased during sintering, the size of β crystal grains also becomes 2 μm or more during sintering, and therefore the grain boundary phase can be obtained only by refining the structure. There was a limit to the reduction.

Further, as disclosed in JP-A-61-191065 and JP-A-2-4406, α'-sialon of the equiaxed crystal grain (general formula M _x (Si, Al) ₁₂ (O , N)
₁₆ and M = Mg, Ca, Li and rare earth elements),
There is also known a method of combining with columnar crystal grains β′-sialon. However, according to the examples described in the publications, these methods also show that any sintered body having a bending strength stably exceeding 100 kg / mm ² is manufactured by the hot pressing method, and is industrially stable. Has not yet achieved high strength characteristics.

[0006] Attempts have been made to improve the strength by dispersing and complexing fine dissimilar particles in the structure of a sintered body of silicon nitride. For example, in the method described in JP-A-4-202059, fine particles of 1 to 500 nm are dispersed in columnar silicon nitride or sialon having a minor axis diameter of 0.05 to 3 μm and an aspect ratio of 3 to 20. However, the strength shown in the example is up to 167 kg / mm.
Although it is ² , since it may contain coarse silicon nitride, strength deterioration is likely to occur, so that the Weibull coefficient is only about 9 and there is a drawback that stable and high strength characteristics cannot be obtained.

Further, Japanese Patent Laid-Open No. 4-295056 discloses that
A method of dispersing different kinds of particles in the grain boundary phase of columnar silicon nitride is disclosed. However, in this case, silicon nitride has a maximum minor axis diameter of 2 to 3.5 μm and a major axis diameter of 10 to 1
Since it reaches 4 μm, the matrix itself becomes a destruction source, the strength of the example is only 158 kg / mm ² at the maximum, and the firing temperature is 1800 ° C. or more, which is satisfactory in terms of productivity and cost. Was not.

[0008]

In view of the above conventional circumstances, the present invention has sufficient strength as a structural material for machine parts, has high reliability with little variation in strength, and has high productivity and cost. It is also an object of the present invention to provide an excellent silicon nitride-based sintered body.

[0009]

In order to achieve the above object, the silicon nitride sintered body provided by the present invention is Si ₃ N ₄
And / or sialon columnar crystal grains and equiaxed crystal grains, a grain boundary phase existing between these crystal grains, and dispersed particles dispersed in the grain boundary phase, and the average of the columnar crystal grains. The minor axis diameter is 0.3 μm or less and the average major axis diameter is 5 μm or less, the equiaxed crystal grains have an average grain size of 0.5 μm or less, and the dispersed particles have an average grain size of 0.1 μm or less. ,
It is characterized in that the volume of dispersed particles is 0.05% by volume or more when the total volume of the other sintered body structures is 1.

[0010]

In the present invention, columnar crystal grains of silicon nitride or sialon and equiaxed crystal grains are used in order to reduce the relative amount of the grain boundary phase that causes strength deterioration in the silicon nitride sintered body. By not only combining and filling, but also dispersing the dispersed particles in the grain boundary phase existing between these crystal grains, the surface area of the grain boundary phase is increased and the amount of the glass phase is relatively decreased. There is. In addition, by including fine dispersed particles in the grain boundary phase, the effect of suppressing the grain growth of the entire structure is recognized, and the size of the columnar crystal grains and the equiaxed crystal grains is controlled to be fine. A uniform structure can be obtained.

As a result, in the silicon nitride-based sintered body of the present invention, the columnar crystal grains of silicon nitride or sialon and the equiaxed crystal grains are made fine and uniform, and at the same time, the amount of grain boundary phase is reduced to form grain boundaries. Since it is possible to reduce the brittleness of JIS,
In the three-point bending strength at room temperature according to R 1601, a strength of 160 kg / mm ² or more is always obtained stably. Further, the silicon nitride-based sintered body of the present invention has excellent machinability,
It was also found to be very useful as a cutting tool.

In order to obtain such excellent strength in a stable manner, columnar crystal grains of Si ₃ N ₄ and / or sialon (β
Crystal) and equiaxed crystal grains (α crystal), and the average minor axis diameter of the columnar crystal grains is 0.3 μm or less and the average major axis diameter is 5 μm.
The average grain size of equiaxed crystal grains is 0.5 μm or less.
It must be: If the average grain size of these crystal grains exceeds the respective upper limit values, the structure becomes non-uniform and the large crystal grains themselves become the fracture source, or the packing density of columnar grains and equiaxed grains is large. Of the grain boundary phase or the thickness of the grain boundary phase is increased, so that the strength of the sintered body is deteriorated.

The dispersed particles dispersed in the grain boundary phase have an average particle diameter of 0.1 μm or less, and the volume of the dispersed particles is 0.05% by volume when the total volume of other sintered body structures is 1. It is necessary to occupy the above. Average particle size of dispersed particle size is 0.1
If it is larger than μm, in addition to existing in the grain boundary phase, the amount existing in the same size as the triple point or equiaxed crystal grains increases,
Since the relative amount of the glass phase of the grain boundary phase cannot be reduced and the grain growth of the entire structure becomes large, the desired strength cannot be obtained.

If the volume of the dispersed particles is less than 0.05% by volume when the total volume of the other sintered body structures is 1, the amount of the glass phase reduced is extremely small, so that the desired strength is also achieved. Can not do it. However, as the volume of the dispersed particles increases, the average particle size also inevitably increases, and it goes without saying that it is necessary to suppress the volume of the dispersed particles so that the average particle size does not exceed 0.1 μm.

Such dispersed particles are compounds other than silicon nitride or sialon, such as Ti, Zr, Hf,
It may be a compound such as V or Cr, and among them, a compound of Ti is preferable. Incidentally, these compounds in the sintered body,
According to the measurement by the X-ray diffraction method, it is recognized that at least a nitride such as TiN is contained.

In particular, when the dispersed particles are titanium compounds, the volume occupied in the sintered body is in the range of 0.05 to 4% by volume in terms of TiN when the total volume of other sintered body structures is 1. Is preferred. If the Ti compound content is less than 0.05% by volume, the desired strength cannot be obtained. If the Ti compound content exceeds 4% by volume, the Ti compounds agglomerate to increase the average particle size and form a defect, so that the desired strength cannot be obtained. . In addition, Ti in the sintered body
When the content of the compound exceeds 4% by volume, the sinterability of the raw material powder deteriorates due to the presence of the Ti compound, so that a non-uniform portion occurs in the structure of the sintered body, leading to a decrease in strength.

To obtain the silicon nitride-based sintered body of the present invention, a sintering aid that reacts with SiO ₂ existing on the surface of the raw material silicon nitride powder to form a liquid phase at a temperature as low as possible,
For example, Y ₂ O ₃ , Al ₂ O ₃ , MgO, CeO ₂ , CaO,
Using spinel or the like, sintering is performed at a temperature of 1650 ° C. or lower in a non-oxidizing atmosphere such as N ₂ gas. Further, it is preferable that the obtained sintered body is secondarily sintered in a non-oxidizing pressurized atmosphere to densify it. The secondary sintering may be performed continuously with the primary sintering, or after the primary room temperature is once cooled to room temperature, the secondary sintering is performed.
Subsequent sintering may be performed.

In the present invention, the compound containing nitride such as TiN, which is the dispersed particles, may be a nitride powder itself such as TiN as a starting material, but the compound is formed during sintering. It is desirable to start with powders of other compounds, for example oxide powders such as TiO ₂ . Particularly when TiO ₂ powder is used as a raw material, the average primary particle size is preferably 0.2 μm or less in order to obtain dispersed particles containing TiN having an average particle size of 0.1 μm or less in the sintered body. .

In the present invention, since the dispersed particles of the Ti compound and the like have the effect of suppressing grain growth during sintering, it is not necessary to use a fine powder having a high α ratio as the raw material silicon nitride powder. It is possible to obtain a fine and uniform structure of columnar β crystal grains of silicon nitride and equiaxed α crystal grains.
Moreover, since the sintering temperature is as low as 1650 ° C. or lower, there is no need to perform sintering in a pressurized atmosphere used to suppress sublimation decomposition of silicon nitride, and pusher type or belt type continuous sintering suitable for mass production. A furnace or the like can be used. Furthermore,
A high-strength sintered body can be easily obtained without using hot isostatic pressing (HIP) sintering. Therefore, the silicon nitride-based sintered body of the present invention is excellent in productivity and cost.

[0020]

Example 1 S having a commercially available average particle size of 0.7 μm and an α ratio of 85%
i ₃ N ₄ powder, and Y ₂ O ₃ powder, Al ₂ O ₃ powder, and MgO powder as sintering aids were mixed in the proportions shown in Table 1 below, and the primary particle diameter was 30 nm as a raw material for dispersed particles. Of T
The iO ₂ powder was blended in a ratio shown in Table 1 in terms of TiN volume conversion when the volume of the entire other sintered body structure was 1.
These powders were wet mixed in ethanol with a nylon ball mill for 100 hours, and then 3000 kg / cm.
CIP molding was performed at ² .

[0021]

[Table 1] Si₃N_Four Y₂O₃ Al₂O₃ MgO TiO₂ sample (wt%) (wt%) (wt%) (wt%) (TiN equivalent vol%) 1 91 5 3 1 0.05 2 91 5 3 1 0.1 3 91 5 3 1 0.5 4 91 5 3 1 2.4 5 91 5 3 1 4.0 6 93 4 2 1 0.3 7 98 1 0.5 0.5 0.2 8 * 91 5 3 1 0 9 * 91 5 3 1 0.01 10 * 91 5 3 1 7.0 11 * 91 5 3 1 10.0 (Note) Samples marked with * in the table are comparative examples.

Next, each of the obtained molded bodies was treated with N _{2 at} 1 atm.
Primary sintering at 1500 ° C. for 4 hours in a gas atmosphere,
Then, in a N ₂ gas atmosphere of 1000 atm, 1
Secondary sintering was carried out at 600 ° C. for 1 hour. Fifteen 3 × 4 × 40 mm bending test pieces were cut out from each of the obtained sintered bodies, each was ground and finished with a # 800 diamond grindstone, and then three points at room temperature in accordance with JIS R 1601. Bending strength was performed to measure average bending strength and Weibull modulus.

In addition, the relative density of each sintered body was determined, and both crystals were obtained from the height of the peak ratio of the columnar α (including α ') and β (including β') crystals by the X-ray diffraction method. The α: β ratio of was determined. Furthermore, after lapping an arbitrary cross section of each sintered body, HF: HNO _{3 at} 80 ° C. = 2: 1
Etching is performed for 30 minutes with the etching solution of, and the magnification is 5
The average grain size of each crystal was determined by observing with a scanning electron microscope of 000 times. The average particle size of the dispersed particles was similarly determined by a transmission electron microscope. The results are shown in Tables 2 and 3.

[0024]

[Table 2] Relative Density Equiaxed Crystal Column-Shaped Crystal Grain Size Dispersed Particle Sample (%) α: β Specific Particle Size (nm) Minor Axis (nm) Major Axis (μm) Particle Size (nm) 1 99.2 15:85 350 250 2.0 30 2 99.4 15:85 300 240 2.0 30 3 99.2 13:87 300 230 2.0 30 4 99.1 9:91 250 200 2.0 50 5 99.4 8:92 250 200 1.5 90 6 99.3 17:83 250 200 2.0 40 7 99.1 17:83 300 250 2.0 30 8 * 99.0 16:84 400 330 2.5 − 9 * 99.0 9:91 320 290 2.5 30 10 * 97.2 9:91 300 300 1.5 350 11 * 96.9 5:95 300 330 1.0 400 (Note ) Samples marked with * in the table are comparative examples.

[0025]

[Table 3]

From the above results, it is understood that each of the samples of the present invention has a high bending strength of 170 kg / mm ² or more and a Weibull coefficient of 22 or more, showing little variation in strength. On the other hand, in Comparative Examples 8 and 9, the strength of the dispersed particles was not improved because the volume of the dispersed particles was too small, and in Samples 10 and 11, the volume of the dispersed particles was too large, and thus the particle diameter of the dispersed particles was large. Therefore, it can be seen that the strength is deteriorated.

EXAMPLE 2 The same raw material powders as in Example 1 were blended in the proportions shown in Table 4 below (Samples 1 and 8 were the same as in Example 1), and each compact was produced in the same manner as in Example 1. Was subjected to primary sintering and secondary sintering under the conditions shown in Table 5 in an N ₂ gas atmosphere.

[0028]

[Table 4] Si₃N_Four Y₂O₃ Al₂O₃ MgO TiO₂ sample (wt%) (wt%) (wt%) (wt%) (TiN equivalent vol%) 2 91 5 3 1 0.1 12 91 5 3 1 0.4 13 89 6 4 1 1.0 14 85 10 4 1 3.0 8 * 91 5 3 1 0 15 * 89 6 4 1 5.0 (Note) Samples marked with * in the table This is a comparative example.

[0029]

[Table 5]

For each of the obtained sintered bodies, as in Example 1, the relative density, the α: β ratio, the average grain sizes of the minor and major axes of the columnar crystals that are α crystals, and the equiaxed shape that is β crystals. Measure the average particle size of crystals and dispersed particles, and
The point bending strength and the Weibull coefficient were measured, and these results are shown in Tables 6 and 7.

[0031]

[Table 6] Relative Density Equiaxed Crystal Column-Shaped Crystal Grain Size Dispersed Particle Sample (%) α: β Specific Particle Size (nm) Minor Axis (nm) Major Axis (μm) Particle Size (nm) 2-A 99.2 16:84 300 230 2.0 30 2-B 99.0 4:96 300 250 1.7 30 2-C 98.8 19:81 350 200 2.5 30 2-D 99.3 10:90 250 200 2.0 30 2-E 99.2 10:90 300 200 2.0 30 12-F 99.5 17:83 200 200 2.5 30 13-G 99.0 16:84 300 250 2.0 60 14-H 98.5 10:90 350 200 1.8 100 14-I 98.9 16:84 350 200 2.3 60 8-J * 97.5 25:75 500 300 1.5-8-K * 98.5 16:84 300 300 1.6-15-L * 96.2 7:93 450 200 1.0 200 15-M * 98.3 1:99 450 350 1.0 200 (Note) * in the table The sample marked with is a comparative example.

[0032]

[Table 7]

Example 3 The same raw material powders as in Example 1 were used, but only the TiO ₂ powder was blended in the proportions shown in Table 8 below, with the primary particle size varied.
Each of the obtained powders was molded in the same manner as in Example 1, each molded body was subjected to primary sintering at 1500 ° C. for 4 hours in a N ₂ gas atmosphere at 1 atm, and subsequently in a N ₂ gas atmosphere at 1000 atm. Secondary sintering was performed at 1600 ° C. for 1 hour.

[0034]

[Table 8] Si₃N_Four Y₂O₃ Al₂O₃ MgO TiO₂ TiO₂ Sample fee (wt%) (wt%) (wt%) (wt%) (TiN equivalent vol%) Primary particle size (nm) 16-1 91 5 3 1 0.2 15 16-2 91 5 3 1 0.2 30 16-3 * 91 5 3 1 0.2 300 17-1 89 5 4 2 0.3 15 17-2 89 5 4 2 0.3 50 17-3 * 89 5 4 2 0.3 200 18-1 89 6 4 1 1.0 100 18-2 * 89 6 4 1 1.0 500 (Note) Samples marked with * in the table are comparative examples.

For each of the obtained sintered bodies, the relative density, the α: β ratio, the average grain sizes of the minor and major axes of the columnar crystals that are α crystals, and the equiaxed shape that is β crystals, as in Example 1. Measure the average particle size of crystals and dispersed particles, and
The point bending strength and Weibull coefficient were measured, and these results are shown in Tables 9 and 10.

[0036]

[Table 9] Relative density Equiaxed crystal column-like crystal grains Size dispersed particles Sample (%) α: β Specific particle size (nm) Minor axis (nm) Major axis (μm) Particle size (nm) 16-1 99.4 11:89 350 250 2.0 15 16-2 99.3 16:84 300 200 2.0 20 16-3 * 97.5 21:79 300 250 1.5 300 17-1 99.5 14:86 250 200 2.0 15 17-2 99.1 15:85 250 200 1.8 50 17-3 * 96.2 16:84 320 250 1.5 250 18-1 99.3 14:86 330 250 2.0 100 18-2 * 98.2 16:84 400 350 1.5 500 (Note) Samples marked with * in the table are for comparison. Here is an example.

[0037]

[Table 10] Bending strength Weibull sample (kg / mm ² ) coefficient 16-1 192 22 16-2 171 20 16-3 * 123 8 17-1 189 23.6 17-2 196 25.3 17-3 * 143 12 18 -1 161 21 18-2 * 139 16.2 (Note) Samples marked with * in the table are comparative examples.

From the above results, when TiO ₂ powder having a large primary particle size is used as the raw material powder for the TiN dispersed particles,
The average particle size of the dispersed particles in the obtained sintered body becomes large,
It can be seen that when the average particle diameter of the dispersed particles exceeds 0.1 μm, the bending strength is lowered and the Weibull coefficient is also lowered, resulting in variations in strength.

Example 4 The same raw material powders as in Example 1 were used, but only the TiO ₂ powder was changed in the primary particle size, and the following Table 11 (Sample 4, Sample 8 and Sample 11 had the same composition as Example 1) was used. It was compounded in the ratio shown in.
Each of the obtained powders was molded in the same manner as in Example 1, each molded body was subjected to primary sintering at 1500 ° C. for 4 hours in a N ₂ gas atmosphere at 1 atm, and subsequently in a N ₂ gas atmosphere at 1000 atm. Secondary sintering was performed at 1575 ° C. for 1 hour.

[0040]

[Table 11] Si₃N_Four Y₂O₃ Al₂O₃ MgO TiO₂ TiO₂ sample (wt%) (wt%) (wt%) (wt%) (TiN equivalent vol%) Primary particle size (nm)  4 91 5 3 1 2.0 15 19 91 5 3 1 0.2 100 8 * 91 5 3 1 0 − 11 * 91 5 3 1 10.0 30 (Note) Samples marked with * in the table are comparative examples.

A cutting tip was produced from each of the obtained sintered bodies and subjected to a cutting test under the conditions shown in Table 12 below. The results of each test are shown in Table 13. The chip life shown in Table 13 was determined by the cutting time until the flank wear width was 0.3 mm.

[0042]

[Table 12]

[0043]

[Table 13]

From the above results, it is understood that the silicon nitride sintered body of the present invention has excellent cutting performance as a cutting tool in both continuous cutting and intermittent cutting.

Example 5 The oxide powders shown in Table 14 below were used as the raw material powders for the dispersed particles, and the same powders as in Example 1 were used as the other raw material powders in the proportions shown in Table 14. 1 for each powder obtained
4 hours at 1500 ° C in N ₂ gas atmosphere at atmospheric pressure
Next sintering was carried out, and then secondary sintering was carried out at 1600 ° C. for 1 hour in a 1000 atm N ₂ gas atmosphere.
The volume of the added oxide is a value converted into a nitride when the entire other structure is 1.

[0046]

[Table 14]

For each of the obtained sintered bodies, the relative density, the α: β ratio, the average grain sizes of the minor axis and the major axis of the columnar crystals that are α crystals, and the equiaxed shape that is β crystals, as in Example 1. Measure the average particle size of crystals and dispersed particles, and
The point bending strength and the Weibull coefficient were measured, and these results are shown in Tables 15 and 16.

[0048]

[Table 15] Relative Density Equiaxed Crystal Column-Shaped Crystal Grain Size Dispersed Particle Sample (%) α: β Specific Particle Size (nm) Minor Axis (nm) Major Axis (μm) Particle Size (nm) 20 99.5 7:93 300 250 2.0 50 21 99.3 8: 92 300 200 1.5 100 22 99.4 10: 90 300 250 1.8 100 23 99.3 5: 95 300 250 1.5 100

[0049]

[Table 16]

[0050]

EFFECTS OF THE INVENTION According to the present invention, a silicon nitride-based sintered body having excellent mechanical strength with an average of three-point bending strength of 160 kg / mm ² or more at room temperature and less variation in strength and high reliability. Can be provided. Further, this silicon nitride-based sintered body has excellent productivity and is very advantageous in terms of cost.

The silicon nitride-based sintered body of the present invention is expected as a material for a mechanical structure, which replaces a conventional metal material, particularly in a field where strength at room temperature is required.
It is also extremely useful as a material for cutting tools.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Yamakawa 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (4)

[Claims] 1. From a columnar crystal grain and an equiaxed crystal grain of Si ₃ N ₄ and / or sialon, a grain boundary phase existing between these crystal grains, and dispersed particles dispersed in the grain boundary phase. The columnar crystal grains have an average minor axis diameter of 0.3 μm or less and an average major axis diameter of 5 μm or less, and the equiaxed crystal grains have an average grain size of 0.5 μm or less, and an average grain size of dispersed particles. Diameter is 0.1
A silicon nitride-based sintered body characterized in that the volume of dispersed particles is at most 0.05% by volume when the total volume of other sintered body structures is 1. 2. The silicon nitride based sintered body according to claim 1, wherein the dispersed particles are a compound of Ti, Zr, Hf, V or Cr. 3. The dispersed particles are a compound of Ti, and the volume thereof is 0.05 to 4% by volume in terms of TiN when the total volume of other sintered body structures is 1. To do
The silicon nitride-based sintered body according to claim 2. 4. The silicon nitride based sintered body according to claim 1, which has a three-point bending strength of 160 kg / mm ² or more at room temperature according to JIS R 1601.